Increasing an integration of a semiconductor device is required to satisfy superior performance and a low price which a consumer requires. In a semiconductor memory device, since integration is an important factor to determine a price of product, a high integration is particularly required. In a case of a conventional two-dimensional or flat semiconductor memory device, since an integration of the device is mainly determined by an area which a unit memory cell occupies, the integration of the device is greatly affected by a technology level of forming a fine pattern. However, since very expensive equipments are needed to realize a miniature of a pattern, a two-dimensional semiconductor memory device has a limitation in increasing integration.
To overcome the limitation, three-dimensional semiconductor memory devices including memory cells three dimensionally arranged have been introduced. However, to mass-produce a three-dimensional semiconductor memory device, a process technology is required, which can realize a reliable product characteristic while manufacturing costs per bit is less than that of a two-dimensional semiconductor memory device.